Tracing the first waves of lymphopoiesis in mice
2006
RAG1/GFP knock-in mice were used to precisely chart the emergence and
expansion of cells that give rise to the immune system. Lymphopoietic cells
detectable in stromal co-cultures arose as early as E8.5, i.e. prior to
establishment of the circulation within the paraaortic splanchnopleura (P-Sp).
These cells were Tie2 + RAG1 - CD34 Lo/-
Kit + CD41 - . While yolk sac (YS) also contained
lymphopoietic cells after E9.5, CD41 + YS cells from ⩽25-somite
embryos produced myelo-erythroid cells but no lymphocytes. Notch receptor
signaling directed P-Sp cells to T lymphocytes but did not confer
lymphopoietic potential on YS cells. Thus, definitive hematopoiesis arises in
at least two independent sites that differ in lymphopoietic potential.
Expression of RAG1, the earliest known lymphoid event, first occurred around
E10.5 within the embryos. RAG1/GFP + cells appeared in the liver at
E11.0 and progenitors with B and/or T lineage potential were enumerated at
subsequent developmental stages.
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